Tamoxifen (brand names Nolvadex, Soltamox) has been used to prevent breast cancer recurrence (return of cancer) in young women with a type of breast cancer called hormone receptor positive breast cancer.
Results presented this week from two large clinical trials reported that premenopausal women with early breast cancer treated with exemestane (brand name Aromasin) had a lower risk of cancer recurrence and of invasive cancer than women treated with tamoxifen.
Both groups of women were also treated to reduce ovarian function because exemestane works better where there is low estrogen — a hormone produced by the ovaries.
"Ask your oncologist about emerging treatments for breast cancer."
Olivia Pagani, MD, clinical director of the Breast Unit at the Oncology Institute of Southern Switzerland in Bellinzona, Switzerland was the lead author of this research.
The research team analyzed the results of two clinical trials — the TEXT and the SOFT trials. These clinical trials enrolled 5,738 premenopausal women who had hormone receptor positive breast cancer.
Within 12 weeks of breast cancer surgery, the women in the study were either treated with exemestane plus ovarian function suppression (OFS) or tamoxifen plus OFS for five years.
The women in the study could choose whether to take triptorelin for five years, have their ovaries removed or receive radiation to their ovaries to achieve OFS.
The aim of this research was to see how many women were disease free in five years and to determine the number of new cancers and breast cancer recurrences and deaths.
At five years, 91 percent of the women who received exemestane plus OFS were free of cancer, compared with 87.3 percent of those who received tamoxifen plus OFS.
The increase in cancer-free survival in the exemestane group represented a 28 percent decrease in five-year cancer risk of the exemestane group compared to that of the tamoxifen group.
There was a 34 percent decrease in breast cancer recurrence in the exemestane group compared to the tamoxifen group.
Five-year survival was high in both groups of women. Almost 96 percent of the women in the exemestane group were alive in five years, and nearly 97 percent of the women who received tamoxifen were alive in five years.
The researchers noted that 14 percent of the women who participated in the studies dropped out, but that this rate was lower than the dropout rate of women taking chemotherapy in everyday practice (not in the study).
The authors concluded that treatment of premenopausal women with hormone receptor positive breast cancer with exemestane plus OFS significantly reduced the chance of breast cancer recurrence compared to treatment with tamoxifen plus OFS.
According to Dr. Pagani, “Our findings indicate that exemestane is better than tamoxifen, when given with ovarian function suppression, but longer follow-up of these young women will be important to assess survival, and any long-term side effects and fertility.”
A scientific abstract of this study was presented June 1 at the annual meeting of the American Society of Clinical Oncology in Chicago, Illinois.
Funding for the research was provided by Pfizer, Ipsen, the International Breast Cancer Study Group and the National Cancer Institute. Several of the study's authors disclosed relationships with the pharmaceutical companies Ipsen, Pfizer and Novartis.